MP1 expression is required for attachment and survival of ER-positive breast cancer cells. Cells were transfected with 40 nM control or MP1 siRNAs as described in Materials and Methods. At 48 h cells were photographed, then harvested for counting and extract preparation. (A) Photographs of MCF-7 cells transfected with two different MP1 siRNA and control siRNA sequences. Scale bar = 100 μm (B) Immunoblots of extracts prepared from cells shown in panel (A). Numbers represent the relative MP1/Actin ratios. (C) Photographs of MCF-7, LCC9 and T47D cells transfected with MP1 siRNA or control siRNA. Scale bar = 100 μm. (D) Immunoblots of extracts prepared from cells shown in panel (C). (E) Attached and floating cells were collected and analyzed as described in Materials and Methods. The percentage of dead cells (black bars) and live cells (white bars) in each population was determined by trypan blue exclusion assays. Data represents the mean ± SD of three independent experiments. Upper error bars indicate the SD for dead cells and lower error bars represent the SD for live cells.